In this image, I’ve covered energy as it passes from the sun in the form of light to the chloroplast of plants. In the chloroplasts, there are structures called thylakoids where the magic happens. This is where photosynthesis takes place in two parts, 1) light-dependent reactions and, 2) Calvin Cycle.

The waste products here are eliminated and the useful products are then sent to the mitochondria. The first step is 1) glycolysis, followed then by 2) the Krebs cycle (also called the Citric Acid Cycle) under aerobic conditions OR, 2) fermentation (under anaerobic conditions)

There’s a LOT of stuff that happens here. These are the basics. This stuff can get extraordinarily complicated–the guy the Krebs cycle is named for won a Nobel prize for his work!

I’ve never, personally seen an image that attempted to go from the sun to photosynthesis to cellular respiration but I tried to keep it as simple as possible. That said, if you feel something’s missing, its probably because it is. Some steps weren’t explicitly mentioned for simplicity’s sake.

One final note: ATP gives you a burst of energy. If you need energy to do anything for longer than about a minute and a half, you want sugar. Sugars provide longer-lasting energy. ATP (which makes up about a half-pound of your total body weight) doesn’t store, in other words, it gets used shortly after it’s made. ATP actually gets recycled over 1,000 times a day by humans!

In your youth was Sesame Street. If you were lucky when you got older there was Bill Nye. Now it would seem you’re too old for education set to music. But if that’s what you think, you’re wrong. Check out these tunes:

Thanks to ProfDodd for the tip – They Might Be Giants sings all things science on their album (that’s a CD for you young’ns) rightfully titled Here Comes Science. Listen to track previews on Amazon.

Rapping is taken to a new level by a couple of guys from Stanford. This video is timely for what we’ve been talking about–ATP, energy, glycolysis–but check out his YouTube page for lots of great videos.

Heterotrophs need to obtain energy from consuming autotrophs. Remember autotrophs turn light energy into chemical energy, which is stored as the sugar glucose. The process of releasing energy by breaking down glucose and other food in the presence of oxygen is called cellular respiration.

Cellular respiration is not exactly, but can be roughly viewed as, the reverse process as photosynthesis. Oxygen and glucose combine to breakdown and reassemble as carbon dioxide, water, and energy.

6O2 + C6H12O6 -> 6CO2 + 6H2O + ATP

oxygen + glucose -> carbon dioxide + water + energy

This process is simplified of course. There’s a whole confusing mess of glycolysis, ATP, and NADH which the average high school bio teacher would want you to know, but honestly it’s overkill (…it’s not even in our state standards…).

Now there are cases when cells don’t get enough oxygen. In this case, the cells produce nasty waste products that they remove from their body. Some microorganisms, such as yeast, produce alcohol in the absence of oxygen. This is called alcoholic fermentation. Other organisms, such as yourself, produce lactic acid in the absence of oxygen. Fittingly, this is called lactic acid fermentation. Fermentation is vital in our food system. Production of alcohol is quite the large business throughout the world; as is production of foods such as yogurt and pickles which utilize lactic acid.

One last point of overkill: the Krebs cycle and electron transport chain. Unless you go to college for Biology, you have no need for this… and honestly, I went to college for Biology and I don’t have a use for it, short of torturing students with it if I was an evil person.

Every organism needs energy to live. But where does that energy come from? Let’s find out…

There are two types of organisms: autotrophs, which make their own food, and heterotrophs, which must consume food from an outside source.

Most autotrophs convert light energy from the sun into usable energy. These are the only types of autotrophs you need to be concerned with for now. Your typical autotroph would be any plant, a grass, a tree, a shrub. Unicellular organisms can be autotrophs too!

Examples of heterotrophs include animals, such as yourself or a lion, as well as fungi plus some unicellular organisms like some protists or bacteria.

Energy comes in many forms. We already mentioned light energy from the sun. There’s also heat energy and other types like the electricity that powers your television.

The type of energy that cells can best use is chemical energy. Specifically it’s in the form of a chemical called ATP. Really the only thing you need to know is that ATP is like a fully charged battery. A bond is broken and energy is released. That turns ATP into ADP. Or you can think of it like this A3P =>release of energy => A2P. ADP is like a battery waiting to be recharged.

ADP + Engery stored = ATP

For some reason this seems to really trip people up. If you have any questions, drop me a comment or a tweet @AmoebaMike.